Thermally expanding sealing elements

ABSTRACT

A sealing element can be used to create a seal in a wellbore or components of a downhole tool. The sealing element can include an elastomer matrix and a substance embedded within the elastomer that expands at a phase change temperature. The substance can be an organic-based substance, such as a polymeric plastic, a thermoplastic, or a wax. The organic-based substance can expand at a temperature greater than or equal to the phase change temperature. The substance can also be a metal-based substance. The metal-based substance can expand at a temperature less than or equal to the phase change temperature. After expansion, the substance can fill small gaps or cracks formed in the elastomer matrix from temperature fluctuations. The sealing element can be included on a downhole tool. The sealing element can be an O-ring or a gasket or included on packer assembly, a plug, or a liner hanger.

TECHNICAL FIELD

A variety of sealing elements can be used to create a seal within awellbore or within wellbore tools or equipment. Thermally expandingmaterials can be included in the sealing elements. The thermallyexpanding materials can expand with an increase or decrease intemperature. After expansion, the thermally expanding materials cancreate a better seal than a sealing element without the thermallyexpanding materials.

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of the various embodiments will be morereadily appreciated when considered in conjunction with the accompanyingfigures. The figures are not to be construed as limiting any of theembodiments.

FIG. 1 is a schematic illustration of a downhole tool including asealing element according to certain embodiments.

FIG. 2 is a schematic illustration of a liner hanger including a sealingelement according to certain embodiments.

FIG. 3 is a schematic illustration of a packer assembly including asealing element according to certain embodiments.

FIG. 4 is a schematic illustration of expansion of two differentthermally expanding materials according to certain embodiments.

DETAILED DESCRIPTION

Oil and gas hydrocarbons are naturally occurring in some subterraneanformations. In the oil and gas industry, a subterranean formationcontaining oil and/or gas is referred to as a reservoir. A reservoir canbe located under land or offshore. Reservoirs are typically located inthe range of a few hundred feet (shallow reservoirs) to a few tens ofthousands of feet (ultra-deep reservoirs). In order to produce oil orgas, a wellbore is drilled into a reservoir or adjacent to a reservoir.The oil, gas, or water produced from a reservoir is called a reservoirfluid.

A well can include, without limitation, an oil, gas, or water productionwell, an injection well, or a geothermal well. As used herein, a “well”includes at least one wellbore. A wellbore can include vertical,inclined, and horizontal portions, and it can be straight, curved, orbranched. As used herein, the term “wellbore” includes any cased, andany uncased, open-hole portion of the wellbore. As used herein, “into awellbore” means and includes into any portion of the well.

A portion of a wellbore can be an open hole or cased hole. In anopen-hole wellbore portion, a tubing string can be placed into thewellbore. The tubing string allows fluids to be introduced into orflowed from a remote portion of the wellbore. In a cased-hole wellboreportion, a casing is placed into the wellbore that can also contain atubing string. A wellbore can contain an annulus. Examples of an annulusinclude but are not limited to the space between the wellbore and theoutside of a tubing string in an open-hole wellbore, the space betweenthe wellbore and the outside of a casing in a cased-hole wellbore, andthe space between the inside of a casing and the outside of a tubingstring in a cased-hole wellbore. It is to be understood that referenceto a “tubing string” includes a casing string.

A variety of wellbore tools are used in oil and gas operations. Thewellbore tools can be run in on a tubing string to perform a variety offunctions. The wellbore tools can include one or more sealing elements.By way of a first example, a sealing element can be used to seal one ormore components of a downhole tool. Non-limiting examples of downholetools that utilize sealing elements include sleeves, valves (e.g.,flapper valves, safety valves, and barrier valves), and seals for toolsthat include an interior space that needs to be separated from wellborefluids, for example, sensors, actuators, telemetry tools, and pressurebalancing seals. The sealing element can seal the one or more componentsof the downhole tools against fluid flow or pressure. Examples of suchsealing elements include but are not limited to O-rings, gland seals,stack seals, and gaskets.

During well completion and production, it is commonly desired to seal aportion of an annulus so fluids will not flow through the annulus butrather flow through the tubing string. By sealing the portion of theannulus, oil, gas, water, or combinations thereof can be produced in acontrolled manner through the wellhead via the tubing string.

By way of a second example, a sealing element can be used to seal aportion of an annulus. Accordingly, a sealing element can be used intools that control fluid flow within an annulus includingcompression-set packers, expanding packers, and liner hangers.Typically, packers are used to anchor the tubing to the wellbore and toseal the tubing to the wellbore. A packer can be used in cased wellboreportions or open-hole wellbore portions. A packer can include a sealingelement that seals to the wellbore to isolate the portion of thewellbore and can also include slips that grip the inside of a tubingstring or wall of the wellbore to anchor the packer to the tubing stringor wellbore wall. The inner diameter (ID) of the sealing element ispositioned around an outer diameter (OD) of an inner mandrel with the IDof the sealing element prevented from disengaging with the OD of theinner mandrel.

Packer sealing elements can be mechanically set, hydraulically set, orhydrostatically set. Other types of packer sealing elements swell in thepresence of a setting fluid. As used herein, the term “set” and allgrammatical variations thereof means the act of causing or allowing adownhole tool to be permanently or retrievably fixed at a desiredlocation within a wellbore—generally by movement of one or more toolcomponents radially away from an inner mandrel and into contact with aninner diameter of a tubing string or wellbore wall.

Setting of the packer energizes the sealing element to expand away fromthe outside of the mandrel to engage with the wall of the wellbore orinside of a tubing string. The packer sealing element is constrained onthe top and bottom such that during setting, the sealing element isforced outward in a direction away from the mandrel. A mechanical packeruses compression of the tubing string to apply the compressive forceneeded to energize the element and slips. A hydraulic packer has aninternal setting piston that is hydraulically actuated to apply thecompression to energize the sealing element and slips. A hydrostatic setpacker has an atmospheric chamber that collapses with well hydrostaticpressure to supply the compressive forces needed to set the packer.

All of these types of packers have a sealing element that is a ring ofelastomeric material with the entirety of the inner diameter of thesealing element fitted onto the outside of a mandrel. The sealingelement is generally constrained on the top and bottom such thatactuation of the packer axially squeezes the sealing element to causeradial expansion of the sealing element and seals the annulus. Theactuation of the packer deploys the slips to grip and anchor the packerto the inside of the tubing string or wall of the wellbore. Forswellable sealing elements, exposure to the setting fluid will cause thesealing element to swell or expand radially away from the inner mandrelto create a seal in the wellbore.

A sealing element can also be used in tools that control fluid flowwithin a tubing string. By way of a third example, a sealing element canbe used to seal a portion of an inside of a tubing string. Plugs, forexample bridge plugs, frac plugs, and seals for plug-and-abandonment,can be used to seal an inside of the tubing string. A plug is composedprimarily of slips, a plug mandrel, and a rubber sealing element. A plugcan be introduced into a wellbore and the sealing element can be causedto block fluid flow into downstream zones when the plug is set much likethe sealing element of a packer.

Packers and plugs can be permanent or retrievable. To retrieve a packeror plug, the sealing element can move back radially towards the innermandrel. In this manner, the sealing element is no longer engaged withthe inside of the wellbore wall or tubing string and allows forretrieval from the wellbore, for example with a retrieval tool. Forpermanent packers or plugs that are not designed to be retrieved fromthe wellbore, it is not necessary for the sealing element to move backtowards the inner mandrel.

A liner hanger is a device used to attach or hang liners from aninternal wall of a previous tubing string. The liner hanger's purpose isto suspend a length of liner inside of the previous tubing string whilesimultaneously sealing the annulus between the liner and the tubingstring. The liner hanger can be anchored to the inside of the tubingstring by contact between metal ridge located around the outside of theliner hanger and the inside of the tubing string. By way of a fourthexample, a sealing element can be used to seal an annulus of a linerhanger.

The bottomhole temperature of a well varies significantly, depending onthe subterranean formation and can range from about 100° F. to about600° F. (about 37.8° C. to about 315.6° C.). As used herein, the term“bottomhole” means at the location of the sealing element. Accordingly,the sealing element can encounter a wide range of temperatures within awellbore. For example, the temperature farther down into a wellbore willgenerally be greater than the temperature up near the wellhead.Therefore, a downhole tool that is moved to different locations withinthe wellbore, either farther away from or closer to the wellhead, canencounter wide temperature fluctuations. Moreover, fluids introducedinto the wellbore or produced from the wellbore can affect thetemperature of wellbore. For example, produced formation fluidsgenerally increase the temperature of the wellbore as the fluids flow upthrough the tubing string towards the wellhead. When production stops,the wellbore cools back down. Conversely, fluids introduced into thewellbore, for example for carbon sequestration, stimulation treatments,and secondary recovery operations, generally decrease the temperature ofthe wellbore as the fluids flow down through the tubing string. Wheninjection of the fluids into the wellbore stops, the wellboretemperature goes back up. It is not uncommon for the temperature withinportions of the wellbore to fluctuate 50° C. or more. In gas injectionwells, such as for carbon sequestration, localized cooling from gasexpansion can decrease the ambient bottomhole temperature to −40° C. orcolder. Steam injection for heavy-oil formations for example can injectfluids that are 400° C. hotter than the ambient bottomhole temperature.

Most sealing elements are made from an elastomer material that iscapable of elastically stretching and can impart structural integrity tothe seal created. However, wide temperature fluctuations can decreasethe structural integrity of the sealing element by causing small gaps orcracks in the elastomer material to form or by decreasing the elasticstrain in the elastomer material or by decreasing the tensile strengthof the elastomer material—especially at the interface between thesealing element and the tool component, wellbore wall, or tubing string.This can compromise the seal whereby pressure is no longer maintainedand/or fluid can bypass the seal.

Some attempts to solve this problem include using seal stacks, which aremultiple sealing elements located adjacent to each other. However, notonly is the use of multiple sealing elements expensive, but also thedimensions of the downhole tool must be increased in order toaccommodate the multiple sealing elements. Thus, there is a need forsealing elements that can maintain structural integrity in environmentswith wide temperature fluctuations.

It has been discovered that a sealing element can include a substancethat expands during or after a phase change. An expanding substance canmaintain structural integrity of the sealing element during temperaturefluctuations. An expanding substance included in the sealing element canfill imperfections in the tubing string, increase the contact stressesagainst the tubing string or downhole tool components, and increase theseal and anchor performance. The additional expansion from the phasechange substance can also help to overcome the elastic recoil from theexpansion process. As used herein, the term “expand,” “expansion,” andall grammatical variations thereof means an increase in the volume ofthe substance. As used herein, a “phase change” means any change thatoccurs to the physical properties of the substance. As used herein, a“phase change” can include, without limitation, a change in the phase ofthe substance (i.e., from a solid to a liquid or semi-liquid, from aliquid or semi-liquid to a solid, from a liquid or semi-liquid to a gas,etc.), a glass transition, a change in the amount of crystallinity ofthe substance, physical changes to the amorphous and/or crystallineportions of the substance, and any combinations thereof. A substancewill undergo a phase change at a “phase change temperature.” As usedherein, a “phase change temperature” includes a single temperature and arange of temperatures at which the substance undergoes a phase change.The “phase change temperature” can be the single temperature or range oftemperatures in which the largest volume expansion occurs. Therefore, itis not necessary to continually specify that the phase changetemperature can be a single temperature or a range of temperaturesthroughout. A material may have multiple phase change temperaturescorresponding to the phase change of different constituents within thematerial.

According to any of the embodiments, a well system comprising: awellbore that penetrates a subterranean formation; and a sealing elementcomprising: an elastomer matrix; and a substance embedded within theelastomer matrix, wherein the substance expands at a phase changetemperature.

According to any of the embodiments, a method of creating a seal withina wellbore comprises: introducing a downhole tool into the wellbore,wherein the downhole tool comprises a sealing element, wherein thesealing element comprises: an elastomer matrix; and a substance embeddedwithin the elastomer matrix, wherein the substance expands at a phasechange temperature; and causing or allowing the sealing element tocreate the seal within the wellbore.

The various disclosed embodiments apply to the systems, methods, andapparatuses without the need to repeat the various embodimentsthroughout. As used herein, any reference to the unit “gallons” meansU.S. gallons.

The well system includes a sealing element. The sealing element can belocated on a downhole tool. The downhole tool can be, for example,sleeves, valves (e.g., safety valves and barrier valves), and seals fortools that include an interior space that needs to be separated fromwellbore fluids, for example, sensors, actuators, telemetry tools, andpressure balancing seals, a packer assembly, a plug, or a liner hanger.

The sealing element can be any type of element that creates a sealbetween two components. By way of a first example, the sealing elementcan create a seal between two components of a downhole tool. Accordingto this example, the sealing element can be without limitation anO-ring, gland seal, stack seal, or gasket. Turning to the Figures, FIG.1 is a schematic illustration of a downhole tool including a sealingelement. It is to be understood that the downhole tool shown in FIG. 1is just one example of a downhole tool that can include a sealingelement as other downhole tools not shown can include the sealingelement. The downhole tool can include a body 213. The body 213 can beconfigured to fit within a tubing string 112. The tubing string 112 andthe downhole tool can be introduced into a wellbore that is defined by awellbore wall 120. An annulus can be defined as the space locatedbetween the wellbore wall 120 and the outside of the tubing string 112and body 213.

The downhole tool can include an inner sleeve 130 and a housing 160. Theinner sleeve 130 can be releasably attached to the housing 160 by afrangible device 147. The downhole tool can also include a valve 141.The valve 141 can be, for example, a flapper valve. The inner sleeve 130and the housing 160 can also include one or more lock rings 133. Thedownhole tool also includes a sealing element 134 that restricts orprevents fluid flow between two or more tool components. By way ofexample and as shown in FIG. 1 , the sealing element 134 can restrict orprevent fluid flow between the outside of the inner sleeve 130 and theinside of the housing 160.

By way of another example, the sealing element can create a seal betweenthe outside of a mandrel of the downhole tool and the inside of a wallof the wellbore or the inside of a tubing string. According to thisexample, the downhole tool can be a packer assembly, a liner hanger, ora plug, and the sealing element can be located around the outside of themandrel of the packer assembly or the plug.

FIG. 2 shows an example of a liner hanger including a sealing element. Atubing system can function as a conduit for a wellbore that penetrates asubterranean formation 102. The tubing system can include a surfacecasing 20 and a surface cement sheath 25 that anchors the surface casing20 in the wellbore. The surface casing 20 can extend from the surface 30down to a desired depth in the well. An intermediate casing 35 can bedeployed concentrically within the surface casing 20. The intermediatecasing 35 can be held in place within the surface casing 20 with anintermediate cement sheath 40. Multiple layers of intermediate casingscan be used. A liner hanger 45 is deployed within the intermediatecasing 35. The liner hanger 45 can suspend a liner 55 from its end. Theliner hanger 45 can be anchored to the intermediate casing 35 with aseries of sealing elements 50. The sealing elements 50 can seal anannulus located between the outside of an inner intermediate casing andthe inside of the adjacent intermediate casing. The seal can inhibit orprevent wellbore fluids from bypassing the liner 55 and liner hanger 45.

The downhole tool can also be a packer. FIG. 3 shows the well during afracturing operation in a portion of a subterranean formation 102. Thesubterranean formation 102 can be penetrated by a well. The wellincludes a wellbore 104. The wellbore 104 extends from the surface 106,and a fracturing fluid 108 is introduced into a portion of thesubterranean formation 102. A pump and blender system 100 can be coupledto a tubing string 112 to pump the fracturing fluid 108 into thewellbore 104 to create one or more fractures 116 in the subterraneanformation 102. The wellbore 104 can include a casing 110 that iscemented or otherwise secured to the wellbore wall. The wellbore 104 canbe uncased or include uncased sections. Perforations can be formed inthe casing 110 or tubing string 112 to allow fracturing fluids and/orother materials to flow into the subterranean formation 102. The wellsystem can include one or more sets of packers 114 that create one ormore wellbore intervals. The packers 114 include a sealing element 118located around the outside of the packers. The sealing element 118 canseal an annulus located between the outside of a tubing string 112 andthe wellbore wall 120.

There can also be more than one sealing element located on the downholetool. For example, a sleeve can include an O-ring and a gasket locatedat different positions on the downhole tool. More than one downhole tool(e.g., a packer assembly and a sleeve) can also include at least onesealing element.

The sealing element includes an elastomer matrix. As used herein, theterm “elastomer” means a natural or synthetic polymer having elasticproperties. As used herein, the term “matrix” means a surrounding mediumor structure. The elastomer of the matrix can be the material in thegreatest concentration of the sealing element and can provide thenecessary structure in which a substance can be embedded within thematrix.

Polymers commonly include amorphous regions and crystalline regions. Apolymer is a large molecule composed of repeating units, typicallyconnected by covalent chemical bonds. A polymer is formed from monomers.During the formation of the polymer, some chemical groups can be lostfrom each monomer. The piece of the monomer that is incorporated intothe polymer is known as the repeating unit or monomer residue. Thebackbone of the polymer is the continuous link between the monomerresidues. The polymer can also contain functional groups or side chainsconnected to the backbone at various locations along the backbone.Polymer nomenclature is generally based upon the type of monomerresidues comprising the polymer. A polymer formed from one type ofmonomer residue is called a homopolymer. A copolymer is formed from twoor more different types of monomer residues. The number of repeatingunits of a polymer is referred to as the chain length of the polymer.The number of repeating units of a polymer can range from approximately11 to greater than 10,000. In a copolymer, the repeating units from eachof the monomer residues can be arranged in various manners along thepolymer chain. For example, the repeating units can be random,alternating, periodic, or block. The conditions of the polymerizationreaction can be adjusted to help control the average number of repeatingunits (the average chain length) of the polymer. As used herein, a“polymer” can include a cross-linked polymer. As used herein, a “crosslink” or “cross linking” is a connection between two or more polymermolecules. A cross-link between two or more polymer molecules can beformed by a direct interaction between the polymer molecules, orconventionally, by using a cross-linking agent that reacts with thepolymer molecules to link the polymer molecules.

A polymer has an average molecular weight, which is directly related tothe average chain length of the polymer. For a copolymer, each of themonomers will be repeated a certain number of times (number of repeatingunits). The average molecular weight for a copolymer can be expressed asfollows:

Avg. molecular weight=(M.W.m ₁*RUm ₁)+(M.W.m ₂*RUm ₂)

where M.W.m₁ is the molecular weight of the first monomer; RU m₁ is thenumber of repeating units of the first monomer; M.W.m₂ is the molecularweight of the second monomer; and RU m₂ is the number of repeating unitsof the second monomer. Of course, a terpolymer would include threemonomers, a tetra polymer would include four monomers, and so on.

The elastomer can be a non-reactive polymer, a degradable polymer, or apolymer that swells in the presence of a fluid, for example, awater-based fluid or an oil-based fluid. Non-limiting examples ofnon-reactive polymers include nitrile rubber, hydrogenated nitrilerubber (HNBR), a fluorocarbon-based fluoroelastomer rubber containingvinylidene fluoride as a monomer such as FKM or FFKM rubbers, naturalrubber, polyetheretherketone rubbers (PEEK), and polytetrafluoroethylene(PTFE), which is a synthetic fluoropolymer of tetrafluoroethylene soldunder the brand name TEFLON®.

Degradable polymers include polymers that dissolve in a wellbore fluid.Non-limiting examples of degradable polymers include urethane,polyurethane rubber, polyether-based rubber, polyester-based rubber,polylactic acid-based polymers, polyglycolic acid-based polymers,polyvinyl alcohol-based polymers, and thiol-based polymers.

Non-limiting examples of swellable polymers include EPDM and rubbersthat are made with super absorbent additives (SAP). EPDM is a copolymermade from ethylene, propylene, and diene co-monomers that enablecrosslinking via sulfur vulcanization. Dienes used in the manufacture ofEPDM rubbers are ethylidene norbornene (ENB), dicyclopentadiene (DCPD),and vinyl norbornene (VNB). EPDM is derived from polyethylene into which45-85 wt % of propylene has been copolymerized to reduce the formationof the typical polyethylene crystallinity. EPDM is a semi-crystallinematerial with ethylene-type crystal structures at higher ethylenecontents, becoming essentially amorphous at ethylene contents thatapproach 50 wt %.

The elastomer matrix polymer can also include more than one type ofpolymer, such as a thermoplastic or thermoset elastomer. Examples of athermoplastic elastomer include thermoplastic urethane, blockcopolymers, thermoplastic olefins, and thermoplastic polyamides.According to a first embodiment, the polymer is a thermoset elastomer inwhich the sealing element is formed from a cast. According to anotherembodiment, the polymer is a thermoplastic polymer in which the sealingelement is molded.

The sealing element can be axially constrained on the top and/or bottomsuch that the sealing element expands in a radial direction only, forexample when the sealing element is included in a packer assembly orplug. The sealing element can also be constrained around the outside ofthe element such that the sealing element expands laterally up and down,for example when the sealing element is an O-ring or gasket. Afterexpansion, the sealing element can create a seal between two or morewellbore components. The elastomer matrix can be energized throughmechanical compression, and according to some of the embodiments, doesnot require an application of pressure to create a seal. According toany of the embodiments, the sealing element creates a seal throughcompression of the sealing element between two surfaces with compressiveloads exceeding 500 pounds force per square inch (psi) for example. Theseal created can form a bi-directional seal wherein the sealing elementcan hold pressure in two directions, for example above and below theseal. According to any of the embodiments, the sealing element iscapable of bi-directionally holding pressures up to 500 psi or greater.

As discussed above, when elastomer sealing elements encounter largetemperature fluctuations (i.e., +/−50° C.), small cracks or voids candevelop in the sealing element and negatively affect the integrity ofthe seal created. By way of example, when a sealing element is tested ata high temperature and then placed in a location having a lowertemperature, the elastomer seems to “take a set” at the high temperatureand has trouble returning to size when cooled. Conversely, elastomerstested at a lower temperature can lose sealing capability when placed ina location having a higher temperature.

The sealing element also includes a substance embedded within theelastomer matrix, wherein the substance expands at a phase changetemperature. The substance expands in volume. The expansion in volumecan occur in one or more dimensions. It is to be understood that unlikea swellable elastomer that swells in the presence of a fluid, thesubstance expands in response to temperature and does not expand orswell in the presence of a fluid. The response and subsequent expansionof the substance can be nearly instantaneous when the substance passesthrough the phase change temperature, for example within seconds orminutes. The expansion of the substance can counteract the negativeeffects of large temperature fluctuations. Other advantages to theexpansion of the substance embedded within the elastomer matrix include,but are not limited to, overcoming compression set in the sealingelement or overcoming elastic recoil in the movement of a mandrelsupporting the elastomer matrix, such as the elastic recoil fromexpanding a liner hanger.

The phase change temperature can be greater than or less than thetemperature at the wellhead. According to any of the embodiments, thesubstance expands with an increase in temperature at or above the phasechange temperature. As used herein, the phrase “expands with an increasein temperature” means a material that expands by more than 5% in volumeas it experiences a phase change from a lower temperature to a highertemperature. The phase change according to these embodiments can be asolid/liquid, solid/semi-liquid, and glass transition. The substance canbe an organic-based substance. The organic-based substance can beamorphous or semi-crystalline in structure. The organic-based substancecan be a polymeric plastic or a thermoplastic including acrylonitrilebutadiene styrene (ABS), polypropylene, nylon 6/6, acetal,polycarbonate, or polyester. A semi-crystalline organic-based substancecan be, for example, high-density polyethylene (HDPE). The organic-basedsubstance can be a wax. The wax can be, for example, a paraffin wax oran animal or plant fat, such as stearic acid. The phase changetemperature for organic-based substances can differ. By way of example,the phase change temperature for paraffin wax can be in the range of 0°C. to 150° C. depending on the composition of the paraffin wax andadditional constituents within the wax, while the phase changetemperature for stearic acid wax can be 70° C., while the phase changetemperature for HDPE can be 125° C. The sealing element can also includemore than one type of organic-based substance, each substance having adifferent phase change temperature, in order to cover a broader range ofbottomhole temperatures. By way of example, the organic-based substancecan include paraffin wax and stearic acid. Table 1 lists non-limitingexamples of volume expansion of different organic-based substances withan increase in temperature.

TABLE 1 Volume Composition Expansion (%) Paraffin 15 Stearic acid 10 ABS12 Polypropylene 28 Nylon 6/6 18 Acetal 21 Polycarbonate 18 Polyester 21HDPE 25

According to any of the embodiments, the substance expands with adecrease in temperature at or below the phase change temperature. Asused herein, the phrase “expands with a decrease in temperature” means amaterial that expands by more than 0.5% in volume as it experiences aphase change from a higher temperature to a lower temperature. FIG. 4 isan illustration of volumetric expansion of paraffin with an increase intemperature and a bismuth alloy with a decrease in temperature. Thephase change temperature according to these embodiments can be thefreezing point of the substance. The phase change according to theseembodiments can be a liquid/solid or semi-liquid/solid. The substancecan a metal-based substance, for example a pure metal or a metal alloy.As used herein, the term “metal alloy” means a mixture of two or moreelements, wherein at least one of the elements is a metal. The otherelement(s) can be a non-metal or a different metal. An example of ametal and non-metal alloy is steel, comprising the metal element ironand the non-metal element carbon. An example of a metal and metal alloyis bronze, comprising the metallic elements copper and tin. Examples ofsuitable metals for the metal-based substance include, but are notlimited to, any pure metals or metal alloys of bismuth, gallium,germanium, or any combination thereof. The metal-based substance may bealloyed with other elements to promote mechanical properties or toadjust the phase change temperature. Alloying elements include silicon,antimony, tin, lead, cadmium, indium, magnesium, manganese, zinc,thallium, mercury, lithium, sodium, and potassium. Properties ofdifferent metals and metal alloys are shown in Table 2 with volumeexpansion with a decrease in temperature.

TABLE 2 Freezing Volume Tensile Point Expansion Strength Composition (°C.) (%) (psi) 100% Ga  29 3.1  2,100 45% Bi; 23% Pb;  47 1.4  5,400 8%Sn; 5% Cd; 19% In 43% Bi; 38% Pb; 71-88 2.0  5,400 11% Sn; 9% Cd 48% Bi;28% Pb; 103-226 1.5 13,000 15% Sn, 9% Sb 55% Bi; 45% Pb 124 1.5  6,400100% Bi 271 3.3%  2,900

The substance can be selected based on the phase change temperature ofthat substance and the anticipated bottomhole temperature increase ordecrease. By way of example, if formation fluids are to be produced andthe bottomhole temperature is anticipated to increase to 200° C. duringproduction, then an organic-based substance having a phase changetemperature of at least 100° C., HDPE for example, can be selected. Inthis manner, when the bottomhole temperature increases to the phasechange temperature of the substance, the substance will undergo thephase change and expand. By way of another example, if fluids are to beinjected into the wellbore and the bottomhole temperature is anticipatedto decrease to 30° C., then a metal-based substance having a phasechange temperature of less than or equal 30° C., pure metal gallium forexample, can be selected.

According to certain embodiments, one or more substance—each of whichhaving a phase change above or below their phase change temperature—canbe used to cover a wide range of bottomhole temperature changes. Forexample, one or more metal-based substances can be selected, whereineach substance undergoes a phase change at or below the freezing pointand each substance has a different phase change temperature. By way ofanother example, one or more organic-based substances can be selected,wherein each substance undergoes a phase change at or above the meltingpoint and each substance has a different phase change temperature. Theseembodiments can be useful when the sealing element is included on adownhole tool that is to be retrieved from the wellbore after use (e.g.,packers or plugs). In this manner, when the bottomhole temperatureincreases or decreases (for example during production or injection) thesubstance can expand and provide a better seal. Then, when thebottomhole temperature reverts back (for example after production orinjection stops), then the substance can contract and no longer be insealing engagement with tool components, the wall of the wellbore, orthe inside of a tubing string. In this manner, the downhole tool can beretrieved.

According to certain other embodiments, two or more substances—onehaving a phase change above its phase change temperature and the otherhaving a phase change below its phase change temperature—can be used tocover a wide range of bottomhole temperature changes. For example, atleast one metal-based substance can be selected and at least oneorganic-based substance can be selected. These embodiments can be usefulwhen the sealing element is included on a downhole tool that is topermanently remain in the wellbore after use (e.g., permanent packers orplugs). These embodiments can also be useful when the seal created isbetween components of the downhole tool and the downhole tool isretrievable (e.g., O-rings or gaskets). In this manner, when thebottomhole temperature increases (for example during production) theorganic-based substance can expand and provide a better seal. Then, whenthe bottomhole temperature cools back down (for example duringinjection), then the metal-based substance can expand and still providea better seal.

The volume expansion of the substance can be different for differentsubstances. According to any of the embodiments, the substance isselected such that the substance expands at least 1%, 3%, or 15% involume. The volume expansion of organic-based substances is generallygreater than metal-based substances as seen in Tables 1 and 2.

Prior to the phase change, the sealing capability of the sealing elementcan be diminished, for example, due to temperature fluctuations duringwellbore operations that create small gaps around and/or throughout thesealing element. According to any of the embodiments, the substanceexpands a sufficient volume such that any small gaps created on thesealing element from temperature fluctuations are filled with thesubstance. Accordingly, after expansion from the phase change, thesealing capability of the sealing element can be restored. The sealingcapability can be restored such that the sealing element is capable ofwithstanding a desired pressure differential. The pressure differentialcan be the bottomhole pressure of the subterranean formation across thesealing element. After the substance undergoes a phase change, then thestrength of the sealing element can increase. By way of example, thebulk modulus of paraffin is roughly 240,000 psi, which indicates thatthe expanding organic-based substance can exert significant force oncomponents and thus strengthen the sealing element.

The substance can be in the form of particles. The particles can have avariety of geometric shapes, such as generally spherical, acicular, orcuboid, and can have generally smooth or jagged perimeters. The size ofthe particles can vary and can range from 10 millimeters (mm) to 1,000nanometers (nm). The particle size can be in the range of 1 mm to 10 nm.The particles are embedded within the elastomer matrix. The particlescan be interspersed throughout the elastomer matrix. The particles canalso be embedded at one or more select regions of the elastomer matrix,for example just around the outer perimeter of the elastomer matrix,where small gaps or cracks are most likely to form due to temperaturefluctuations.

The sealing element can be located on the downhole tool adjacent to asecond sealing element that does not include the substance. Thisembodiment can be useful if the substance reduces the overall strengthof the sealing element. In this manner, the use of a second sealingelement can ensure adequate seals are created.

The substance particles can also include other materials in addition tothe phase change substance. For example, non-reactive strengtheners canbe added to the organic-based substance. Fibers or other particles canbe used to increase the stiffness of the metal-based substance. Theconcentration of other materials can be selected such that the sealingcapabilities of the sealing element are maintained after the phasechange. For example, including other materials at a higher concentrationreduces the amount of the phase change substance that is available forexpansion.

There is a potential for some waxes to seep out of the elastomer matrixat high temperatures. If the wax seeps out of the elastomer matrix, thenthe wax would no longer provide long-term sealing enhancement fromexpanding. According to any of the embodiments, the organic-basedsubstance particles are encapsulated in a shell. The shell can be usedto keep the wax as a distinct phase within the elastomer matrix. Thematerials for the shell can be oil incompatible so the shell materialdoes not seep out the elastomer matrix. The shell material can stretch.In this manner, when the substance expands during the phase change, theshell will not crack and provide a path for the substance to seep out ofthe elastomer matrix. The shell material can be selected from polymericmaterials comprising acrylic, epoxy, silver, polystyrene, carbonnanotubes, silicon dioxide, fluorocarbon-based fluoroelastomer (FKM), orpolytetrafluoroethylene (PTFE), which is a synthetic fluoropolymer oftetrafluoroethylene sold under the brand name TEFLON®.

The methods include introducing the downhole tool within the wellbore.The well can be, without limitation, an oil, gas, or water productionwell, an injection well, or a geothermal well. The well can also be anoffshore well. The methods can include causing or allowing thebottomhole temperature of the wellbore to decrease. The decrease intemperature can be performed after the downhole tool is introducedwithin the wellbore. The step of decreasing can include introducing afluid into the wellbore or cessation of producing formation fluids. Thefluid can be a variety of types of fluids used in oil or gas operations,for example, drilling fluids, injection fluids, fracturing fluids,work-over fluids, acidizing fluids, gravel packing fluids, completionfluids, and stimulation fluids. According to this embodiment, the fluidbeing introduced into the wellbore has a surface temperature that isless than the phase change temperature of the substance. By way ofexample, fracturing fluids can cool the bottomhole temperature of thewellbore by over 100° F. (37.8° C.). The temperature of the portion ofthe wellbore can be decreased to a temperature that is less than orequal to the phase transition temperature of the metal-based substance.

The methods include causing or allowing the bottomhole temperature ofthe wellbore to increase. The bottomhole temperature can be increased byintroducing a fluid into the wellbore, producing a fluid from thewellbore, or cessation of pumping a colder fluid into the wellbore. Thefluid can have a temperature greater than or equal to the phase changetemperature of the substance. According to any of the embodiments, thephase change of the substance occurs within the normal operatingbottomhole temperatures encountered during the oil or gas operation.Normal operating bottomhole temperatures encountered can range from

-   -   −40° C. to 550° C. or from 4° C. to 200° C. depending on the        specific oil or gas operation performed.

The following are two, non-limiting examples of uses of the sealingelement with a metal-based substance that expands when the temperaturedecreases below the phase change temperature. According to a firstexample, the sealing element is placed on the outside of a casing. Theheat of curing cement located in an annulus between the casing and thewall of the wellbore causes the phase-change of the metal from a solidto a liquid, which results in the contraction of the metal-basedsubstance, and consequently a reduced volume of the elastomer matrix,which allows more cement to fill the annular gap. After the curing iscomplete and the bottomhole temperature decreases, the metal-basedphase-change material expands and helps to seal any potential annulargaps between the casing and the cement. According to a second example,the sealing element is part of a frac plug. The wellbore is warm whenthe plug is installed, and the metal-based substance is liquid, whichallows for a low setting force. During a fracturing operation, theinjected water cools the frac plug and solidifies the metal-basedsubstance. The metal expands as it solidifies and enhances the seal. Thesolidified metal also increases the stiffness of the elastomer matrix,which increases the pressure holding capability of the plug.

The following are two, non-limiting example of uses of the sealingelement with an organic-based substance that expands when thetemperature increases above the phase change temperature. According to afirst example, a packer including the sealing element is introduced intoa geothermal well. The organic-based substance is solid when set. As hotwater is produced from the geothermal wellbore, the organic-basedsubstance expands and increases the integrity and pressure holdingcapability of the seal. According to a second example, a liner hangerincludes the organic-based substance in at least one of the sealingelements. The liner hanger is expanded into position and set to sealbetween the outside of a tubing string and the inside of another tubingstring. As the subterranean formation heats up the sealing element, theorganic-based substance expands and helps to overcome any elastic recoilthat may have occurred during the setting of the liner hanger.

An embodiment of the present disclosure is a well system comprising: awellbore that penetrates a subterranean formation; and a downhole toolcomprising a sealing element, wherein the sealing element comprises: anelastomer matrix; and a substance embedded within the elastomer matrix,wherein the substance expands at a phase change temperature. Optionally,the well system further comprises wherein the downhole tool is selectedfrom a sleeve, a valve, a sensor, an actuator, a telemetry tool, apressure balancing seal, a packer assembly, a plug, or a liner hanger.Optionally, the well system further comprises wherein the sealingelement creates a seal between components of the downhole tool, andwherein the sealing element is an O-ring, gland seal, stack seal, orgasket. Optionally, the well system further comprises wherein thesealing element creates a seal between an outside of a mandrel of thedownhole tool and the inside of a wall of the wellbore or the inside ofa tubing string, and wherein the downhole tool is a packer assembly, aliner hanger, or a plug. Optionally, the well system further compriseswherein the elastomer of the elastomer matrix is a non-reactive polymer,a degradable polymer, or a polymer that swells in the presence of afluid. Optionally, the well system further comprises wherein thesubstance expands with an increase in temperature at or above the phasechange temperature. Optionally, the well system further compriseswherein the substance is an organic-based substance. Optionally, thewell system further comprises wherein the organic-based substance isselected from the group consisting of: a polymeric plastic; athermoplastic comprising acrylonitrile butadiene styrene, polypropylene,nylon 6/6, acetal, polycarbonate, or polyester; a semi-crystallineorganic-based substance; or a wax comprising paraffin or stearic acid.Optionally, the well system further comprises wherein the sealingelement further comprises a second organic-based substance, wherein thesecond organic-based substance has a different phase change temperaturethan the organic-based substance. Optionally, the well system furthercomprises wherein the organic-based substance is in the form ofparticles, and wherein the particles are encapsulated in a shell.Optionally, the well system further comprises wherein the substanceexpands with a decrease in temperature at or below the phase changetemperature. Optionally, the well system further comprises wherein thesubstance is a metal-based substance. Optionally, the well systemfurther comprises wherein the metal-based substance comprises puremetals or metal alloys comprising bismuth, gallium, germanium, silicon,antimony, tin, lead, cadmium, indium, magnesium, manganese, zinc,thallium, mercury, lithium, sodium, potassium, and combinations thereof.Optionally, the well system further comprises wherein the sealingelement further comprises a second metal-based substance, wherein thesecond metal-based substance has a different phase change temperaturethan the metal-based substance. Optionally, the well system furthercomprises wherein the substance expands with an increase in temperatureat or above the phase change temperature, and wherein the sealingelement further comprises a second substance, wherein the secondsubstance expands with a decrease in temperature at or below the phasechange temperature. Optionally, the well system further compriseswherein the substance is selected such that the substance expands atleast 1% in volume. Optionally, the well system further compriseswherein the substance is in the form of particles having a particle sizein the range of 10 millimeters to 1,000 nanometers. Optionally, the wellsystem further comprises wherein the particles are interspersedthroughout the elastomer matrix.

Another embodiment of the present disclosure is a method of creating aseal within a wellbore comprising: introducing a downhole tool into thewellbore, wherein the downhole tool comprises a sealing element, whereinthe sealing element comprises: an elastomer matrix; and a substanceembedded within the elastomer matrix, wherein the substance expands at aphase change temperature; and causing or allowing the sealing element tocreate the seal within the wellbore. Optionally, the method furthercomprises wherein the downhole tool is selected from a sleeve, a valve,a sensor, an actuator, a telemetry tool, a pressure balancing seal, apacker assembly, a plug, or a liner hanger. Optionally, the methodfurther comprises wherein the sealing element creates a seal betweencomponents of the downhole tool, and wherein the sealing element is anO-ring, gland seal, stack seal, or gasket. Optionally, the methodfurther comprises wherein the sealing element creates a seal between anoutside of a mandrel of the downhole tool and the inside of a wall ofthe wellbore or the inside of a tubing string, and wherein the downholetool is a packer assembly, a liner hanger, or a plug. Optionally, themethod further comprises wherein the elastomer of the elastomer matrixis a non-reactive polymer, a degradable polymer, or a polymer thatswells in the presence of a fluid. Optionally, the method furthercomprises wherein the substance expands with an increase in temperatureat or above the phase change temperature. Optionally, the method furthercomprises wherein the substance is an organic-based substance.Optionally, the method further comprises wherein the organic-basedsubstance is selected from the group consisting of: a polymeric plastic;a thermoplastic comprising acrylonitrile butadiene styrene,polypropylene, nylon 6/6, acetal, polycarbonate, or polyester; asemi-crystalline organic-based substance; or a wax comprising paraffinor stearic acid. Optionally, the method further comprises wherein thesealing element further comprises a second organic-based substance,wherein the second organic-based substance has a different phase changetemperature than the organic-based substance. Optionally, the methodfurther comprises wherein the organic-based substance is in the form ofparticles, and wherein the particles are encapsulated in a shell.Optionally, the method further comprises wherein the substance expandswith a decrease in temperature at or below the phase change temperature.Optionally, the method further comprises wherein the substance is ametal-based substance. Optionally, the method further comprises whereinthe metal-based substance comprises pure metals or metal alloyscomprising bismuth, gallium, germanium, silicon, antimony, tin, lead,cadmium, indium, magnesium, manganese, zinc, thallium, mercury, lithium,sodium, potassium, and combinations thereof. Optionally, the methodfurther comprises wherein the sealing element further comprises a secondmetal-based substance, wherein the second metal-based substance has adifferent phase change temperature than the metal-based substance.Optionally, the method further comprises wherein the substance expandswith an increase in temperature at or above the phase changetemperature, and wherein the sealing element further comprises a secondsubstance, wherein the second substance expands with a decrease intemperature at or below the phase change temperature. Optionally, themethod further comprises wherein the substance is selected such that thesubstance expands at least 1% in volume. Optionally, the method furthercomprises wherein the substance is in the form of particles having aparticle size in the range of 10 millimeters to 1,000 nanometers.Optionally, the method further comprises wherein the particles areinterspersed throughout the elastomer matrix.

Another embodiment of the present disclosure is a downhole toolcomprising: a mandrel; and a sealing element located adjacent to themandrel, wherein the sealing element comprises: an elastomer matrix; anda substance embedded within the elastomer matrix, wherein the substanceexpands at a phase change temperature. Optionally, the downhole toolfurther comprises wherein the downhole tool is selected from a sleeve, avalve, a sensor, an actuator, a telemetry tool, a pressure balancingseal, a packer assembly, a plug, or a liner hanger. Optionally, thedownhole tool further comprises wherein the sealing element creates aseal between components of the downhole tool, and wherein the sealingelement is an O-ring, gland seal, stack seal, or gasket. Optionally, thedownhole tool further comprises wherein the sealing element creates aseal between an outside of a mandrel of the downhole tool and the insideof a wall of the wellbore or the inside of a tubing string, and whereinthe downhole tool is a packer assembly, a liner hanger, or a plug.Optionally, the downhole tool further comprises wherein the elastomer ofthe elastomer matrix is a non-reactive polymer, a degradable polymer, ora polymer that swells in the presence of a fluid. Optionally, thedownhole tool further comprises wherein the substance expands with anincrease in temperature at or above the phase change temperature.Optionally, the downhole tool further comprises wherein the substance isan organic-based substance. Optionally, the downhole tool furthercomprises wherein the organic-based substance is selected from the groupconsisting of: a polymeric plastic; a thermoplastic comprisingacrylonitrile butadiene styrene, polypropylene, nylon 6/6, acetal,polycarbonate, or polyester; a semi-crystalline organic-based substance;or a wax comprising paraffin or stearic acid. Optionally, the downholetool further comprises wherein the sealing element further comprises asecond organic-based substance, wherein the second organic-basedsubstance has a different phase change temperature than theorganic-based substance. Optionally, the downhole tool further compriseswherein the organic-based substance is in the form of particles, andwherein the particles are encapsulated in a shell. Optionally, thedownhole tool further comprises wherein the substance expands with adecrease in temperature at or below the phase change temperature.Optionally, the downhole tool further comprises wherein the substance isa metal-based substance. Optionally, the downhole tool further compriseswherein the metal-based substance comprises pure metals or metal alloyscomprising bismuth, gallium, germanium, silicon, antimony, tin, lead,cadmium, indium, magnesium, manganese, zinc, thallium, mercury, lithium,sodium, potassium, and combinations thereof. Optionally, the downholetool further comprises wherein the sealing element further comprises asecond metal-based substance, wherein the second metal-based substancehas a different phase change temperature than the metal-based substance.Optionally, the downhole tool further comprises wherein the substanceexpands with an increase in temperature at or above the phase changetemperature, and wherein the sealing element further comprises a secondsubstance, wherein the second substance expands with a decrease intemperature at or below the phase change temperature. Optionally, thedownhole tool further comprises wherein the substance is selected suchthat the substance expands at least 1% in volume. Optionally, thedownhole tool further comprises wherein the substance is in the form ofparticles having a particle size in the range of 10 millimeters to 1,000nanometers. Optionally, the downhole tool further comprises wherein theparticles are interspersed throughout the elastomer matrix.

Therefore, the various embodiments are well adapted to attain the endsand advantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thevarious embodiments may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is, therefore, evident thatthe particular illustrative embodiments disclosed above may be alteredor modified and all such variations are considered within the scope andspirit of the present invention.

As used herein, the words “comprise,” “have,” “include,” and allgrammatical variations thereof are each intended to have an open,non-limiting meaning that does not exclude additional elements or steps.While compositions, systems, and methods are described in terms of“comprising,” “containing,” or “including” various components or steps,the compositions, systems, and methods also can “consist essentially of”or “consist of” the various components and steps. It should also beunderstood that, as used herein, “first,” “second,” and “third,” areassigned arbitrarily and are merely intended to differentiate betweentwo or more zones, sealing elements, etc., as the case may be, and donot indicate any sequence. Furthermore, it is to be understood that themere use of the word “first” does not require that there be any“second,” and the mere use of the word “second” does not require thatthere be any “third,” etc.

Whenever a numerical range with a lower limit and an upper limit isdisclosed, any number and any included range falling within the range isspecifically disclosed. In particular, every range of values (of theform, “from about a to about b,” or, equivalently, “from approximately ato b,” or, equivalently, “from approximately a-b”) disclosed herein isto be understood to set forth every number and range encompassed withinthe broader range of values. Also, the terms in the claims have theirplain, ordinary meaning unless otherwise explicitly and clearly definedby the patentee. Moreover, the indefinite articles “a” or “an,” as usedin the claims, are defined herein to mean one or more than one of theelements that it introduces. If there is any conflict in the usages of aword or term in this specification and one or more patent(s) or otherdocuments that may be incorporated herein by reference, the definitionsthat are consistent with this specification should be adopted.

1. A well system comprising: a wellbore that penetrates a subterraneanformation; and a downhole tool comprising a sealing element, wherein thesealing element comprises: an elastomer matrix; and a substance embeddedwithin the elastomer matrix, wherein the substance expands at a phasechange temperature, wherein the substance expands with a decrease intemperature at or below the phase change temperature, wherein thesubstance is a metal-based substance consisting of pure metals selectedfrom bismuth, gallium, or germanium or consisting of a metal alloy,wherein the metal alloy comprises bismuth, gallium, or germanium in thegreatest percentage of the metal alloy.
 2. The well system according toclaim 1, wherein the downhole tool is selected from a sleeve, a valve, asensor, an actuator, a telemetry tool, a pressure balancing seal, apacker assembly, a plug, or a liner hanger.
 3. The well system accordingto claim 1, wherein the sealing element creates a seal betweencomponents of the downhole tool, and wherein the sealing element is anO-ring, gland seal, stack seal, or gasket.
 4. The well system accordingto claim 1, wherein the sealing element creates a seal between anoutside of a mandrel of the downhole tool and the inside of a wall ofthe wellbore or the inside of a tubing string, and wherein the downholetool is a packer assembly, a liner hanger, or a plug.
 5. The well systemaccording to claim 1, wherein an elastomer of the elastomer matrix is anon-reactive polymer, a degradable polymer, or a polymer that swells inthe presence of a fluid. 6.-13. (canceled)
 14. The well system accordingto claim 1, wherein the sealing element further comprises a secondmetal-based substance, wherein the second metal-based substance has adifferent phase change temperature than the metal-based substance. 15.The well system according to claim 1, wherein the sealing elementfurther comprises a second substance, and wherein the second substanceexpands with an increase in temperature at or above a phase changetemperature.
 16. The well system according to claim 1, wherein thesubstance is selected such that the substance expands at least 1% involume.
 17. The well system according to claim 1, wherein the substanceis in the form of particles having a particle size in the range of 10millimeters to 1,000 nanometers.
 18. The well system according to claim17, wherein the particles are interspersed throughout the elastomermatrix.
 19. A method of creating a seal within a wellbore comprising:introducing a downhole tool into the wellbore, wherein the downhole toolcomprises a sealing element, wherein the sealing element comprises: anelastomer matrix; and a substance embedded within the elastomer matrix,wherein the substance expands at a phase change temperature, wherein thesubstance expands with a decrease in temperature at or below the phasechange temperature, wherein the substance is a metal-based substanceconsisting of pure metals selected from bismuth, gallium, or germaniumor consisting of a metal alloy, wherein the metal alloy comprisesbismuth, gallium, or germanium in the greatest percentage of the metalalloy; and causing or allowing the sealing element to create the sealwithin the wellbore.
 20. A downhole tool comprising: a mandrel; and asealing element located adjacent to the mandrel, wherein the sealingelement comprises: an elastomer matrix; and a substance embedded withinthe elastomer matrix, wherein the substance expands at a phase changetemperature, wherein the substance expands with a decrease intemperature at or below the phase change temperature, wherein thesubstance is a metal-based substance consisting of pure metals selectedfrom bismuth, gallium, or germanium or consisting of a metal alloy,wherein the metal alloy comprises bismuth, gallium, or germanium in thegreatest percentage of the metal alloy.
 21. The well system according toclaim 15, wherein the second substance is an organic-based substance.22. The well system according to claim 21, wherein the organic-basedsubstance is selected from the group consisting of: a polymeric plastic;a thermoplastic comprising acrylonitrile butadiene styrene,polypropylene, nylon 6/6, acetal, polycarbonate, or polyester; asemi-crystalline organic-based substance; or a wax comprising paraffinor stearic acid.
 23. The well system according to claim 21, wherein theorganic-based substance is in the form of particles, and wherein theparticles are encapsulated in a shell.
 24. The downhole tool accordingto claim 20, wherein an elastomer of the elastomer matrix is anon-reactive polymer, a degradable polymer, or a polymer that swells inthe presence of a fluid.
 25. The downhole tool according to claim 20,wherein the sealing element further comprises a second metal-basedsubstance, wherein the second metal-based substance has a differentphase change temperature than the metal-based substance.
 26. Thedownhole tool according to claim 20, wherein the sealing element furthercomprises a second substance, and wherein the second substance expandswith an increase in temperature at or above a phase change temperature.27. The downhole tool according to claim 26, wherein the secondsubstance is an organic-based substance.
 28. The downhole tool accordingto claim 27, wherein the organic-based substance is selected from thegroup consisting of: a polymeric plastic; a thermoplastic comprisingacrylonitrile butadiene styrene, polypropylene, nylon 6/6, acetal,polycarbonate, or polyester; a semi-crystalline organic-based substance;or a wax comprising paraffin or stearic acid.